Dear all:
Now we design a board integrated a TMS320C6678 and Micron DDR3 for signal processing. We use a TPS54620 for their both 1.5V power supply, and get the VREF （0.75V） of the DDR3 by the resistance divider. We measured the power noise of the 1.5V：the common ripple Vpp is less than 10mV, but the noise grows radpidly to more than 70mV when the DDR3 performs self-refreshing. To decrese this noise, we add lots of the capacitor including bulk and high-freqnecy ceramic capacitors, but there is no effect at all.
Now we are not sure if this situation has any nagetive effect for the DDR3 operations?
P.S. In another design, we used TPS56221 for the 1.5V power supply, and the noise is only 40mV when the DDR3 performs self-refreshing. So is the transient response of the DC-DC chip affacting the noise?
Really hope experts to explain this, and we will so appriciate for your help!
